Emissive cathode



July 31, 1956 J. KATZBERG 2,757,309

EMISSIVE CATHODE Filed Sept. 24, 1953 F I G. I I0 I t II I l IZ I IO F I G. 3

EMISSIVE COATING JESSE KATZBERG INVENTOR ATTORNEY United States Patent Ofice 2,757,309 iatented July 31, 1956 2,757,309 EMISSIVE CATHODE Jesse Katzberg, Tenafly, N. J., assignor to Gera Corporation, New York, N. Y., a corporation of New Jersey This invention relates to emissive coatings for cathodes in discharge devices and has particular reference to an intermediate layer of emissive material which provides a secure bond between the cathode base electrode and the outer emissive coating.

Emissive cathodes for electron discharge devices have been constructed by depositing the emissive coating directly on the surface of the metallic base electrode. Such a structure is generally good enough to perform well in all applications such as radio receiving sets, phonograph reproducers, and medium power transmitting applications. However, it has been found that in cases where the devices are subjected to severe shock, the emissive coating applied directly to the metal may become loose and fall ofi. The present invention provides a structure for emissive coatings which will withstand severe shock and, in addition, possesses other desirable features not found in the conventional type of cathode.

One of the objects of this invention is to provide an improved emissive cathode coating which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to protect the cathode coating from becoming loose and falling off when the tube is subjected to severe shock.

Another object of the invention is to provide an emissive coating which will not sputter when subjected to severe ion bombardment in gas-filled discharge devices.

Another object of the invention is to increase the shock resistant qualities of cathode coatings without lowering the efficiency of the electron emission.

Another object of the invention is to provide an emissive coating for cathodes which can be used either in a highly exhausted vacuum tube or in a gas-filled discharge device.

One feature of the invention includes an intermediate coating of barium titanate which is applied to the cathode electrode. The usual emissive coating of barium and strontium carbonates is deposited on the surface of the barium titanate.

Another feature of the invention includes a single coating of a mixture of barium titanate and the emissive carbonates.

Another feature of the invention includes a first coating of a mixture of the barium titanate and the emissive carbonates and a second coating of the emissive carbonates alone.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

Fig. 1 is a plan view of a heater type cathode with parts cut away to show the internal construction.

Fig. 2 is a side view of a vacuum tube diode showing a filamentary cathode.

Fig. 3 is a cross sectional view of the cathode.

Fig. 4 is a cross sectional view of an alternate cathode.

Referring now to the drawings, Figs. 1 and 3 show a cathode having a hollow cylindrical metal base with a heater element 11 inserted in the hollow tubular cavity. A first coating of barium titanate 12 is deposited on the metal base 10 and may be any thickness which produces the desired working characteristics. by experiment that a coating .0001 satisfactory amount.

A second coating 13 composed of the usual mixture of barium and strontium carbonates is deposited on the surface of the barium titanate. A small amount of binder may be added to the mixture but for this type of cathode a binder is not necessary. The thickness of the emissive coating should conform to the usual practise in the manufacture of vacuum and gas tubes and may be of the order of 10 milligrams of deposited material per square centimeter.

After the cathode is formed it is mounted in a vacuum tube and the usual baking-out processes are applied. During the exhaust routine the deposited coatings are heated sufiiciently to produce a close adhering bond between the metal and the barium titanate and between the barium titanate and the emissive coating.

It has been found to .0005 inch is a still retains the same shock resistant qualities. This coating arrangement is shown in Fig. 4 and comprises a hol low cylindrical metal base 10, a heater 11 within the mechanical strength of the coating, causing it to adhere to the metallic base and to resist flaking and sputtering due to mechanical shock and ionic bombardment.

Fig. 2 shows a diode vacuum tube having an envelope 15, an anode 16, and a filamentary cathode 17 which is coated with an emissive coating of the structure shown in Figs. 3 or 4.

It is well known that any emissive coating may be combined with a small percentage of a neutral binder mateafiecting the efliciency of emission. manner barium titanate may be combined with small percentages of other neutral materials without aifecting either its adhering or emissive qualities.

While there have been described and illustrated specific embodiments of the invention, it will be obvious that modifications may be made therein without departing from the field of the invention which should be limited only by the scope of the appended claims.

I claim:

stance on the barium titanate.

2. A thermionic emissive electrode comprising,

References Cited in the file of this patent UNITED STATES PATENTS 

1. A THERMIONIC EMISSIVE ELECTRODE COMPRISING, A CONDUCTIVE BASE, AN INTERMEDIATE COATING ON THE BASE WHICH INCLUDES BARIUM TITANATE AND AN ELECTRON EMISSIVE SUBSTANCE ON THE BARIUM TITANATE 